Genetic factors are being researched under the Human Genome Project. The three major research sources being used are:
Genetic Mapping: locating sequences of genes on chromosomes that may indicate traits and/or disorders.
Physical Mapping: a complicated process of further identifying specific genes.
Sequence Mapping: creating a sequence map of all three-billion DNA bases of the human genome so that specific genes can be identified.
Bio/Neurological factors are also being researched under three major resources:
1. Studies of the neurotransmitter, which include chemicals in the brain that deliver neural impulses from one neuron to another.
The 40 year search for neurotransmitter abnormalities in Autism has no firm conclusion. The only constant result across numerous neurotransmitter studies involving children with Autism has been the finding of elevated Serotonin levels in peripheral blood in about a fourth of the individuals studied. A biochemical cause for Schizophrenia also has been suspected for over a century with no single neurotransmitter being identified. A single neurotransmitter hypothesis of Schizophrenia has been rejected as evidence for the involvement of multiple neurotransmitters has increased. Serotonin deficiency has been found to be connected to obesity, obsessive-compulsive disorder, eating disorders, social phobias, premenstrual syndrome, anxiety and panic, migraines, and even extreme violence. However, most brain functions appear to result from the multiple influences of several different neurotransmitters.
2. Organic causes, which include structural abnormalities in the brain.
A variety of organic etiologies for Autism, Depression, and Schizophrenia have been proposed. Organic causes for Autism were concluded by some of the earliest researchers in studying this certain population of children. Even though definitive neurological abnormalities have not been demonstrated, there is considerable evidence that the etiology of Autism resides in the operation of a neurological factor or factors. Individuals with Autism are more likely to demonstrate neurological "soft signs," persistent primitive reflexes, abnormalities on an EEG and a brain scan, and an increased likelihood of Seizures. Neurological dysfunction has also been found in patients suffering from Depression, indicating a biophysical attendant of Depression that has yet to be specified. The main structural findings appear to be enlarged lateral ventricles and decreased volume in the frontal lobe and part of the subcortical structures. More recent research supports this conclusion, and suggests that Depression results from a complex interaction of brain structure, brain function, metabolic activity, and environmental factors.
3. Studies of Metabolism.
Phenylketonuria (PKU) is one of the many disorders that highlight the importance of the metabolic system in the mediation of learning and behavior. PKU is a recessive genetic disorder that causes the body to be unable to metabolize the protein phenylalanine. When uncontrolled by diet, this disorder is characterized by severe mental retardation, convulsions, and behavioral problems, among other symptoms. Benjamin Feingold, a pediatric allergist from California, developed the concept of food allergies as a causative factor of ADHD. Becoming interested in in allergies after treating adverse reactions to aspirin, he and his associates began to suspect widespread allergic reactions to salicylates, a natural compound that is contained in many fruits and has a structure very similar to aspirin. With this hypothesis, Feingold came up with a strict diet, Feingold Diet, that he claimed should be successful in decreasing symptoms in "about 50% of hyperkinetic-learning disabled children," or ADHD.
Temperament factors refer to a certain behavioral style that is an inborn tendency but also highly influenced by the environment the child grows and lives in. It emerges primarily from a longitudinal study that began in 1965 by Alexander Thomas, Stella Chess, Herbert G. Birch, Margaret Hertzig and Sam Korn to follow a sample of over a hundred children from infancy to adulthood. Thomas and his colleagues identified nine characteristics of temperament that were stable and endured through maturity. They include: activity level, regularity (of biological functions), adaptability, threshold of responsiveness, intensity of reaction, mood quality, distractibility, persistence, and attention span. From these nine characteristics, three major patterns emerged that accounted for 65% of the children: the easy child, accounting for 40% of the sample, the difficult child, account for 10% of the sample, and the slow-to-warm-up child, which accounted for 15% of the sample. The remaining 35% showed no consistent temperament patterns.